1. Field of the Invention
The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a technique for achieving a high-definition display in a device which displays different images towards each of a plurality of viewpoints.
2. Description of the Related Art
In accordance with developments in mobile phones and information terminals, size reduction and high-definition imaging of image display devices are being advanced. In the meantime, as an image display device having a new added value, image display devices with which an observer can visually recognize different images depending on observing positions, i.e., an image display device with which different images can be visually recognized at a plurality of viewpoints and a stereoscopic image display device with which an observer can visually recognize an image three-dimensionally by making different images as parallax images on left and right sides, are drawing attentions.
As a method for proving different images from each other towards a plurality of viewpoints, there is known a method which displays an image by interlacing image data for each of viewpoints on a display panel, separates the displayed interlaced image by an optical separating module constituted with a lens and a barrier (a light-shielding plate) having slits, and provides the images to the respective viewpoints. The principle of image separations is implemented by restricting pixels viewed in each of viewpoint directions by using an optical module such as a barrier having slits or a lens. As the image separation module, generally used are a parallax barrier constituted with a barrier having a great number of stripe slits and a lenticular lens in which a great number of cylindrical lenses exhibiting the lens effect in one direction are arranged.
The stereoscopic image display device using the optical image separating module is suited to be loaded on a terminal device such as a mobile phone in respect that it is not necessary for users to wear special eyeglasses so that the users are free from having a trouble of wearing the eyeglasses. Portable phones on which a stereoscopic image display device constituted with a liquid crystal panel and a stereoscopic image display device have already been developed into manufactured products.
With the above-described method, i.e., with the stereoscopic image display device which provides different images from each other towards a plurality of viewpoints by using an optical separating module, there are cases where borders between images are viewed dark when the image to be visually recognized is switched because the viewpoint position of the observer is shifted. This phenomenon is caused due to a fact that a non-display area (a light-shielding part called as a black matrix in general in a liquid crystal panel) between the pixels for each of the viewpoints is visually recognized. The above-described phenomenon caused in accordance with the shift in the viewpoint of the observer does not occur with a general stereoscopic image display device that has no optical separating module. Thus, the observer feels a sense of discomfort or deterioration of the display quality for the above-described phenomenon that occurs in a multi-viewpoint stereoscopic image display device or a stereoscopic image display device having an optical separating module. This is a phenomenon generally called as “3D moire”.
In order to improve the issue caused due to the optical separating module and the light-shielding part, there is proposed a stereoscopic image display device which suppresses the deterioration of the display quality through devising shapes and layout of the pixel electrode and the light-shielding part of the display panel (e.g., Japanese Unexamined Patent Publication 2005-208567 (FIG. 37, etc.) (Patent Document 1).
FIG. 50 is a plan view showing a display panel of a display device disclosed in Patent Document 1. In FIG. 50, drawn are cylindrical lenses 1003a, first viewpoint pixels 1041, aperture parts 1075, wirings 1070, second viewpoint pixels 1042, light-shielding parts 1076, longitudinal direction 1011, lateral direction 1012, and the like. In the display device disclosed in Patent Document 1, the proportion of the light-shielding parts (the wiring 1070 and the light-shielding part 1076) and the aperture parts 1075 is substantially constant, when a display panel sectional view is assumed along the longitudinal direction that is vertical to the arranging direction of the cylindrical lenses 1003a at an arbitrary point of the lateral direction 1012.
Therefore, even when the observer shifts the viewpoint in the lateral direction 1012 that is the separating direction of the image so that the observing direction becomes changed, the proportion of the light-shielding part to be visually recognized is substantially constant. That is, the observer does not observe only the light-shielding part from a specific direction and, further, the display is not viewed dark. In other words, deterioration of the display quality caused due to the light-shielding region can be prevented.
Now, “3D moire” and “3D crosstalk” will be described in details. In this Specification, periodic luminance unevenness (may also mean color unevenness in some cases) caused when displaying different videos in different angular directions, particularly fluctuation in the angular direction of luminance (luminance angular fluctuation), is defined as “3D moire”, and an amount of leak of a image for the left or the right eye into the respective other eye is defined as “3D crosstalk”.
In general, a stripe pattern generated when structures of different periods from each other interfere with each other is called as “moire fringes”. The moire fringes are an interference fringes generated depending on the periodicity and pitch of the structures. In the meantime, “3D moire” is luminance unevenness generated due to an image forming characteristic of the image separating module. Thus, in this Specification, “3D moire” and “moire fringes” are used in a distinctive manner.
There may be cases where “3D moire” is not an issue, depending on the visually recognizing positions. However, when there is a large fluctuation in the luminance angular direction, it is considered that there is an influence that is not preferable for stereoscopic visions. Thus, it is preferable to set the luminance fluctuation to be equal to or lower than a prescribed amount. Further, when the amount of “3D crosstalk” becomes great, a stereoscopic sense is lost and an influence may be imposed on the observer such as fatigue of the eyes. Thus, it is preferable to set the crosstalk amount to be equal to or lower than a prescribed amount.
Incidentally, a multi-domain vertical aligned (referred to as “MVA” hereinafter) method as one of liquid crystal display modes exhibits a wide viewing angle characteristic, and is used widely (WO 2008069181 (Patent Document 4) and Japanese Unexamined Patent Publication 2010-146008 (Patent Document 5), for example). With this MVA method, a liquid crystal exhibiting negative dielectric anisotropy is aligned almost vertical to a substrate. Further, it is so designed that the tilt directions of the liquid crystal when a voltage is applied are divided into a plurality of different regions. The liquid crystal molecules in the divided regions compensate the viewing angle characteristics of each other, so that wide viewing angles can be acquired. There is Japanese Unexamined Patent Publication 2004-302315 (FIG. 1, etc.) (Patent Document 2) as an example of implementing a stereoscopic image display device by using the MVA method.
FIG. 51 is an explanatory chart of a stereoscopic image display device according to Patent Document 2. The right side of FIG. 51 is a lateral sectional schematic view of a main part of a liquid crystal panel 2017. The left side of FIG. 51 is an optical conceptual view 2018 which shows images (2010a, 2010b, 2011a, 2011b) reflected on the left and right eyes of the observer who looks at the liquid crystal panel 2017 from the front side. In the liquid crystal panel 2017, a protrusion 2006 is provided on a TFT (thin film transistor) substrate 204 as a domain restricting structure for locally restricting the alignment of liquid crystal molecules 2007. On both of left and right sides (on top and bottom on the sheet) of the protrusion 2006, pixel electrodes 2009A and 2009B formed with divided ITO (indium tin oxide) transparent electrodes are provided. In the meantime, a common electrode 2008 formed with an ITO transparent electrode is provided on a surface of a color filter substrate 2003 opposing to the TFT substrate 2004. A liquid crystal exhibiting negative dielectric anisotropy is inserted between the color filter substrate 2003 and the TFT substrate 2004. Further, a vertical alignment film (not shown) is provided to cover the surfaces of both of the opposing ITO transparent electrodes, respectively. Furthermore, polarization plates 2001 and 2002 are disposed on the surfaces of the color filter 2003 and the TFT substrate 2004, respectively, in a crossed-Nicol state. Individual signal voltages 2005A and 2005B are applied between the common electrode 2008 and the pixel electrodes 2009A, 2009B. The regions corresponding to the pixel electrodes 2009A and 2009B are domains 2000A and 2000B, respectively.
In a state where a voltage is not applied, the liquid crystal panel 2017 displays “black” because the liquid crystal molecules 2007 are aligned vertically on the surface of the ITO transparent electrodes. In accordance with an applied voltage, the liquid crystal molecules 2007 are tilted in the opposite directions from each other with respect to the protrusion 2006 as the domain restricting structure, thereby forming the domains 2000A and 2000B shown in the drawing. Under such alignment state, light at an angle close to be in parallel to the length direction of the liquid crystal molecules 2007 exhibits small deflection caused by the optical anisotropy. Thus, the transmission amount of the light becomes small, so that it is radiated as weak light. In the meantime, light at an angle close to be vertical to the length direction of the liquid crystal molecules 2007 exhibits large deflection caused by the optical anisotropy. Thus, the transmission amount of the light becomes large, so that it is radiated as strong light. In FIG. 51, the weak light radiated from the domain 2000A is shown by a dotted-line arrow 2013, and the weak light radiated from the domain 2000B is shown by a dotted-line arrow 2016. In the meantime, the strong light radiated from the domain 2000A is shown by a solid-line arrow 2015, and the strong light radiated from the domain 2000B is shown by a solid-line arrow 2014. Angle θ of the radiated light with respect to a normal 2019 of the liquid crystal panel 2017 is the viewing angle.
An image signal captured from a camera placed at the position of the right eye is sent to the domains 2000A of each pixel via an applied voltage 2005A simultaneously, while an image signal captured from a camera placed at the position of the left eye is sent to the domains 2000B of each pixel via an applied voltage 2005B simultaneously. Upon this, a bright image 2010b by the strong light 2014 radiated from each of the domains 2000B and a dark image 2010a by the weak light 2013 radiated from each of the domains 2000A are formed simultaneously on the retina of the left eye of the observer who looks at the liquid crystal panel 2017 from the front side. In the meantime, a bright image 2011a by the strong light 2016 radiated from each of the domains 2000A and a dark image 2011b by the weak light 2016 radiated from each of the domains 2000B are formed simultaneously on the retina of the right eye. However, only the bright images 2010b and 2011a on the left and right eyes are fused in the head and the dark images by the weak light are unconsciously ignored, so that the observer who looks at the liquid crystal panel 2017 from the front side see an optical illusion as if a stereoscopic image emerges on the liquid crystal panel 2017. In a moving picture, this illusion is more prominent. A condition under which such phenomenon occurs is that the light amount of the weak light is equal to or less than ½ of the light amount of the strong light. Desirably, it is equal to or less than 1/10.
In the meantime, as an example of a case which achieves a multiple view display by using a vertical alignment as a liquid crystal display mode, there is Japanese Unexamined Patent Publication 2008-261980 (FIG. 1, etc.) (Patent Document 3).
A multiple view display 3001 shown in FIG. 52 and FIG. 53 includes: a liquid crystal panel 3004 including a display device 302 and an optical device 3003 provided integrally with the display device 3002; and a backlight, not shown, which radiates planar white light to the display device. The display device 3002 is formed by interposing a liquid crystal layer 3007 between an array substrate 3005 and a counter substrate 3006 disposed by facing the array substrate 3005, which forms a rectangular display region including sub-pixels P as a plurality of pixels formed in matrix. Further, polarization plates 3008 and 3009 are laminated on the main surfaces on the outer side of the substrates 3005 and 3006, respectively.
The display device 3002 can display a plurality of different images by the use of a drive circuit, not shown. That is, among the plurality of sub-pixels P, two pixel groups are formed with a pixel group constituted with a plurality of sub-pixels Pa and a plurality of sub-pixels Pb located alternately by one column each in the direction such as the left-and-right directions towards which the image is separated by the parallax, for example. This makes it possible to display individual images by each of the pixel groups.
The array substrate 3005 includes a plurality of scan lines 3012 and a plurality of signal lines 3014 on a transparent substrate 3011 in a grating form, and a TFT 3015 is provided at each intersection between the scan line 3012 and the signal line 3014. Further, an insulating layer 3016 is provided to cover the TFT 3015, a pixel electrode 3018 provided on the insulating layer 3016 is electrically connected to the TFT 3015 via a contact hole 3017 provided to the insulating layer 3016, and a vertical alignment film 3019 for aligning liquid crystal molecules LC that constitute the liquid crystal layer 3007 is formed on the pixel electrode 3018.
The pixel electrode 3018 is formed with ITO, and formed for each sub-pixel. Further, a slit S is formed between the neighboring pixel electrodes 3018, respectively. The TFT 3015 is constituted with a source electrode 3015s, a drain electrode 3015d, a gate electrode 3015g, a semiconductor layer 3015p, and the like.
In the counter substrate 3006, a color filter layer 3022 having colored layers 3022r, 3022g, and 3022b corresponding to the three primary colors RGB is formed on the transparent substrate 3021. Further, on the color filter layer 3022, a counter electrode 3023 formed with ITO is formed at positions corresponding to each sub-pixel P. Three sub-pixels P corresponding to the colored layers 3022r, 3022g, and 3022b of the color filter layer 3022 constitute a single pixel unit.
Further, a rib-shaped counter protrusion 3025 is formed, respectively, at prescribed positions of the counter electrodes 3023. Furthermore, a vertical alignment film 3026 for aligning the liquid crystal molecules LC is formed by covering the counter electrodes 3023 and the counter protrusions 3025.
The sectional view of the counter protrusion 3025 is formed in a triangular shape whose tip is projected towards the array substrate 3005 side, and formed linearly along the end of two sub-pixels Pa, Pb which are neighboring to each other on the left and right sides and corresponding to different images. Therefore, the counter protrusion 3025 is provided for every two sub-pixels Pa, Pb.
The liquid crystal layer 3007 is of an MVA type which exhibits negative dielectric anisotropy. Further, the liquid crystal molecules LC among the liquid crystal materials constituting the liquid crystal layer 3007 are designed to be aligned along the right direction of FIG. 52 for the sub-pixel Pa and the left direction of FIG. 52 for the sub-pixel Pb, i.e., along the opposite directions for the neighboring sub-pixels Pa and Pb, under a state where a voltage is applied between the pixel electrode 3018 and the counter electrode 3023. In order to achieve such alignment design, utilized are the existence of the counter protrusions 3025, effects such as the tilt of the electric field on the outer side of the slits S by the electric field discretion effect between the pixel electrode 3018 and the counter electrode 3023, etc. That is, The alignment directions of the liquid crystal molecules LC is set by corresponding to the viewing angle directions from which the different display images are visually recognized, and the liquid crystal layer 3007 is divided into a plurality of domains for each of the neighboring sub-pixels Pa and Pb.
In the meantime, the optical device 3003 separates the image so that each of the images displayed on the display device 3002 is visually recognized only along prescribed directions. In the optical device 3003, a parallax barrier layer 3032 as the light-shielding part and a slit part 3033 as a transmission part are formed on the transparent substrate 3031. Further, the optical device 3003 is bonded to the display surface side that is the opposite side of the liquid crystal layer 3007 of the transparent substrate 3021 that constitutes the counter substrate 3006 via an adjusting layer 3034 as a refractive index adjusting layer formed by a transparent adhesive or the like.
The parallax barrier layer 3032 is for shielding the light of the images by pixel groups in the direction different from the viewing angle direction, and it is formed with chrome as a non-light transmitting metal or a resin into which a black pigment such as carbon black is dispersed. The parallax barrier layer 3032 is formed by corresponding to a position between the two sub-pixels Pa and Pb which are neighboring to each other on the left and right sides and corresponding to different images. Therefore, one each of the parallax barrier layer 3032 is provided for a single domain at a position superimposing on (opposing to) the counter protrusion 3025.
Through writing different signals with a pixel group constituted with a plurality of sub-pixels Pa and a pixel group constituted with a plurality of sub-pixels Pb located alternately by each column along the direction (left-and-right direction of FIG. 52) that separates an image by the parallax, the state of the liquid crystal molecules LC of each domain changes from the vertical state to the tilted state according to the image signals.
As a result, when viewed from a prescribed viewing angle direction L1, an image displayed with the pixel group of the plurality of sub-pixels Pb with a surface light radiated from a backlight is shielded at the parallax barrier layer 3032, and the image displayed with the pixel group of the plurality of sub-pixels Pa is visually recognized from the slit parts 3033 via each of the colored layers 3022r, 3022g, and 3022b of the color filter layer 3022.
In the meantime, when viewed from a prescribed viewing angle direction R1, an image displayed with the pixel group of the plurality of sub-pixels Pa with a surface light radiated from a backlight is shielded at the parallax barrier layer 3032, and the image displayed with the pixel group of the plurality of sub-pixels Pb is visually recognized from the slit parts 3033 via each of the colored layers 3022r, 3022g, and 3022b of the color filter layer 3022.
At this time, light passed through the color filter layer 3022 of each of the colors RGB is visually recognized in each of the viewing angle directions L1 and R1, so that images of those colors are mixed and visually recognized as a color image.
When the viewing angle is largely shifted and viewed from the viewing angle directions L2 and R2 shifted in the left-and-right directions of the drawing with respect to the viewing angle directions L1 and R1, respectively, the liquid crystal molecules LC are aligned in the reverse directions and viewed only as black even when the sub-pixel Pa or the sub-pixel Pb neighboring to each other comes into the viewing angle. Thus, it is not likely to be visually recognized as image crosstalk.
With the stereoscopic image display device depicted in Patent Document 2, it is not possible to implement the stereoscopic display intended by the document in a fine manner.
Regarding the viewing angle characteristics of the vertical alignment liquid crystal, Patent Document 2 utilizes the region where the characteristics become asymmetric when the angles are fixed to given azimuth directions (e.g., 0-degree and 180-degree directions, 90-degree and 270-degree directions within a display face) and the angle of depression (polar angle when expressed as polar coordinates) is changed. Such azimuthal angle directions normally include the direction to which the liquid crystal molecules are tilted by the electric field. Regarding the vertical alignment liquid crystal of this case, FIG. 54 shows an example of the viewing angle characteristics in the polar angle direction of the luminance. In this drawing, shown are the viewing angle characteristics in the polar angle directions (written as the tilt angles in the drawing) of the luminance when the voltage to be applied to the liquid crystal is changed as 0 V, 2 V, 3 V, 4 V, and 5 V. Considering the condition of a voltage of 3 V, the luminance at the tilt angle of 30 degrees is equal to or higher than 30, and the luminance at the tilt angle −30 degrees is about 3. When those are used in combination, the condition of the light amount equal to or less than 1/10 described in the section of related technique regarding Patent Document 2 can be satisfied.
However, considering the condition of a voltage of 5 V, the luminance at the tilt angle of 30 degrees is equal to or higher than 30, and the luminance at the tilt angle −30 degrees is about 25. Thus, even the condition of the light amount equal to or less than ½ described in the section of the related technique cannot be satisfied. Further, considering the condition of a voltage of 2 V, the luminance at the tilt angle of 30 degrees is about 0.2, and the luminance at the tilt angle −30 degrees is about 5.5. Thus, it is completely opposite characteristic from the condition of the light amount described in the section of the related technique. As described, for satisfying the condition of the light amount depicted in Patent Document 2 by using the vertical alignment liquid crystal, the voltages are limited to an extremely narrow range. Therefore, it is not practical, and a fine stereoscopic display cannot be achieved.
With the multiple view display depicted in Patent Document 3, it is not possible to achieve the multiple views intended by the document in a fine manner.
As in the case of Patent Document 2, Patent Document 3 utilizes the fact that the viewing angle characteristics in a given azimuth angle direction of the vertical alignment liquid crystal become asymmetric. Regarding a case where a parallax barrier layer is provided in the vertical alignment liquid crystal as depicted in Patent Document 3, FIG. 55 shows an example of the viewing angle characteristics in the polar angle direction of the luminance. Note here that in the barrier layer, the transmission region and the non-transmission region are arranged to be disposed alternately in the direction where the pixel Pa and the pixel Pb are disposed alternately as depicted in the section of the related technique regarding Patent Document 3. That is, it is so designed that the transmission region and the non-transmission region of the barrier layer are arranged alternately in the direction that is orthogonal to the border between the pixel Pa and the pixel Pb as a set.
In the chart, two conditions of 2 V and 5 V are shown as the voltage to be applied to the liquid crystal. A case of shifting the viewing angle greatly to the angle of 40 degrees or more will be investigated. The luminance is close to 35 at 5 V between 40 degrees and 45 degrees. In the meantime, the luminance is about 18 at 5 V between 40 degrees and 50 degrees. The luminance is decreased about to a half from 45 degrees to 50 degrees. However, it is not deteriorated down to a state of black display as mentioned in the section of the related technique and the image can be fully recognized, thereby generating image crosstalk. That is, in the vicinity of 45 degrees, the luminance is equal to or higher than 10, and crosstalk of about 30% for the maximum luminance of about 35 is generated. Further, when the characteristic at a voltage of 2 V is considered, the luminance from 40 degrees to 45 degrees is about 1.3, while the luminance from 45 degrees to 50 degrees is about 16. This relationship is completely opposite from the characteristic of 5 V, and the state of the image crosstalk becomes greatly different by a halftone. This means that a proper image cannot be recognized. As described, it is difficult to satisfy the condition of Patent Document 3 by using the vertical alignment liquid crystal and the barrier layer, and a fine multiple view display cannot be achieved.
A structure which achieves a wide viewing angle stereoscopic image display by combining the technique depicted in Patent Document and the MVA method will be investigated, although it is not a related technique. Considered is a case of achieving 2-viewpoints color stereoscopic image display device using a right-eye image and a left-eye image is achieved by the pixel structure of FIG. 50. In that case, it is considered to employ a structure that uses a display unit, which is constituted with six sub-pixels of three colors lined along the longitudinal direction as the right-eye sub-pixels and the left-eye sub-pixels as in FIG. 56A by corresponding to each of the colors of red, blue, and green by using a color filter corresponding to each of those colors, as the minimum repeating unit. Symbols are allotted to each of the sub-pixels by using R for the right-eye image, L for the left-eye image, r for red, b for blue, and g for green. For example, Rr is a right-eye red sub-pixel, and Lb is left-eye blue sub-pixel.
In a case of employing the MVA method for the pixel alignment, it is necessary to divide each sub-pixel into four domains having different liquid crystal alignment. This is for improving the viewing angle characteristic when viewing the display face from the top and bottom as well as left-and-right directions. That is, a single display unit, i.e., the six sub-pixels, is divided into twenty-four domains in total. This divided state can be conceptually shown as in FIG. 56B. For example, the sub-pixel Lr is constituted with four domains Lr1, Lr2, Lr3, and Lr4.
However, each of the regions becomes small with this structure, so that it is difficult to divide it into different liquid crystal alignment. This is because it becomes difficult to control the structure and the processing for dividing to the different liquid crystal alignment in small regions. For example, as such structure, there is a structure which controls the electric fields of the projection structure projected from the substrate surface, the slit, the projection part, or the like of the electrodes. As such processing, there are light alignment processing, surface anisotropic processing, i.e., surface processing such as mask rubbing or the like using a mask, etc. Another reason is that the extremely small divided regions of different liquid crystal alignment tend to contract the border towards the minimum energy state so that the energy in the border between the divisions becomes small. Thus, as the border is contracted, the divided regions themselves may rapidly become contracted. Therefore, it is desired for the divided alignment regions to be in a size of more than a specific size.
As a result, when high definition of the pixels is advanced, it becomes extremely difficult to employ the MVA method with the pixel structure of Patent Document 1.
An exemplary object of the present invention is to provide a liquid crystal display device which is capable of achieving a stereoscopic display and a multi-view display with high definition and in a wide viewing angle range. The multi-view display is a display with which different images are observed depending on the observing directions. For example, it is used in a manner where information viewed from the right side of a display device and information viewed from the left side thereof is different. Further, an exemplary object of the present invention is to provide a liquid crystal display device which can achieve a stereoscopic display in which 3D moire and 3D crosstalk are decreased. Another exemplary object of the present invention is to provide a liquid crystal display device capable of switching a stereoscopic display and a multi-view display to a 2D single display, which can achieve the wide viewing angle characteristic in both the stereoscopic display as well as the multi-view display and the 2D single display. A yet another exemplary object of the present invention is to provide a liquid crystal display device capable of achieving a stereoscopic display and a multi-view display with a wide viewing angle range, which can be manufactured easily at a reduced cost.